It is necessary and desirable for filter cartridges to have a bypass in case filter media in the filter cartridge becomes clogged so that the machine utilizing the fluid being filtered is not starved for fluid. For example, it is necessary for filter cartridges which filter lubricating oil used in internal combustion engines not to block the flow of oil to the engine if their filter media becomes clogged. It is also desirable to prevent oil from draining out of a filter cartridge when the fluid is not under pressure. For example, with internal combustion engines if the engine is not running, it is preferable to maintain oil in the cartridge so that when the engine is restarted, oil is immediately available for circulation.
It is also desirable to prevent unscrupulous filter installers from filling replacement filter cartridges with used or unfiltered oil.
During manufacture, when disparate parts are matched, the risk of failure is increased because one of the parts may be of inferior quality and adversely affect the reliability of the entire assembly. It is frequently time consuming and therefore costly to assemble a plurality of elements in order to configure an item reliably. Consequently, utilizing only a single element can be advantageous. This is especially the case with mass produced OEM and after market items such as filters for engine lubricating oil which are manufactured by the millions.